Space shuttle Discovery's final mission is delayed again due to additional small cracks on the shuttle's tank. The mission is now off until late February.

Managers are evaluating potential launch dates for space shuttle Discovery in late February and working to see if International Space Station on orbit operations would allow a launch as early as Feb. 24. More will be known next week and managers hope to set a launch date by the end of next week, the National Aeronautics and Space Administration (NASA) said in a statement on Jan. 7.

Progress continues to be made in understanding the most probable cause of cracks discovered on the space shuttle's external tank mid-section, known as the intertank, where small cracks developed during the Nov. 5, 2010, launch attempt.

After Discovery shuttle was returned to the Vehicle Assembly Building before Christmas, four additional small cracks were found during thorough X-ray of the backside of the tank.

NASA is considering reinforcing all 108 struts on the central part of the tank for extra safety, NASA spokesman Allard Beutel said Friday.

Plans are for the repair work to continue through the weekend. The shuttle program also reviewed the plan to modify as many as 32 additional stringers, which is expected to be complete next week, with radius blocks, which will provide added structural support in areas known to carry much of the structural load of the external tank, NASA stated on Jan. 7.

These radius blocks essentially fit over existing stringer edges through which the securing rivets are installed to provide additional structural support. The radius block modification is a known and practiced structural augmentation technique used extensively on the intertank, NASA said.

NASA managers will meet with Space Shuttle Program officials today to review the progress to date and the forward plan. A determination of the need and viability for the installation of additional radius blocks on all balance stringers will be made sometime next week.

With the work remaining, the potential for additional modifications yet to be defined, and further reviews pending, the decision was made Thursday to allow the teams additional time and delayed the targeted launch date out of the early February launch window. Launch dates for Discovery and Endeavour will be discussed at this week Thursday’s Space Shuttle Program Requirements Control Board meeting.

The space shuttle Discovery's mission will deliver and install the Permanent Multipurpose Module Leonardo, the Express Logistics Carrier 4 and also provide critical spare components to the International Space Station.

When first flown in 1984, Discovery became the third operational orbiter, and is now the oldest orbiter in service. Discovery has flown 38 flights, completed 5,247 orbits, and has spent 322 days in orbit.

Discovery is the orbiter fleet leader, having flown more flights than any other orbiter in the fleet, including four in 1985 alone. Discovery flew all three 'return to flight' missions after the Challenger and Columbia disasters: STS-26 in 1988, STS-114 in 2005, and STS-121 in 2006.

After the orbiter has retired, Discovery will be offered by NASA to the Smithsonian Institution's National Air and Space Museum for public display and preservation as part of the national collection. Discovery will replace Space Shuttle Enterprise in the Smithsonian's display at the Steven F. Udvar-Hazy Center.

The STS-133 crew will deliver robot Robonaut 2 (R2) to the International Space Station. Cocooned inside an aluminum frame and foam blocks cut out to its shape, R2 is heading to the station inside the Permanent Multipurpose Module in space shuttle Discovery's payload bay.

Designed by NASA and General Motors as a robotic assistant for astronauts working in space, R2 looks like the upper torso of a sculpted bodybuilder and is topped with a helmeted head that includes two cameras to give it three-dimensional vision plus other sensors.

It will be the first humanoid robot in space, and although its primary job for now is teaching engineers how dexterous robots behave in space, the hope is that through upgrades and advancements, it could one day venture outside the station to help spacewalkers make repairs or additions to the station or perform scientific work.

R2, as the robot is called, will launch inside the Leonardo Permanent Multipurpose Module, which will be packed with supplies and equipment for the station and then installed permanently on the Unity node.

Once R2 is unpacked -- which is likely several months after it arrives -- it will initially be operated inside the Destiny laboratory for operational testing, but over time both its territory and its applications could expand. There are no plans to return R2 to Earth, said NASA.